1. Field of the Invention
Systems and methods consistent with the present invention relate to a digital transmission system and a data transmission method thereof. More particularly, the present invention relates to a digital transmission system which transmits a transmission signal into which a low power signal expressing additional data is inserted, and a data transmission method thereof.
2. Description of the Related Art
As electronic and communication technology has developed, digital technology has been introduced into the field of broadcasting systems and diverse standards for digital broadcasting have been released. The diverse standards include a U.S. Advanced Television System Committee (ATSC) Vestigial Sideband (VSB) standard and a European Digital Video Broadcasting-Terrestrial (DVB-T)standard. These standards have differences in many aspects, such as their audio compression schemes and channel bands, but the main difference is that the ATSC VSB standard uses a single-carrier scheme and the DVB-T standard uses a multi-carrier scheme. In particular, the DVB-T standard adopts an Orthogonal Frequency Division Multiplexing (OFDM) method as a standard in order to reduce interference between channels.
OFDM transmits data using a multi-carrier, converts a serially input symbol row into parallel data streams, and modulates each stream with a plurality of orthogonal sub-carriers.
A single-carrier transmission scheme in which data are carried in a single carrier and transmitted has high interference between symbols, so distortion increases. As a result, the complexity of an equalizer in a receiver increases. OFDM is introduced in order to solve this problem of the single-carrier transmission scheme.
As described above, efforts have been made worldwide to provide effective transmission and reception of broadcast signals using digital technology. Specifically, data transmission methods, such as wireless local area network (LAN), code division multiple access (CDMA), time division multiple access (TDMA), or methods using a cable, are used.
Data, such as broadcast signals and other signals, as well as additional data can be transmitted to televisions (TVs). For example, urgent rescue text broadcasting must be transmitted to TV viewers even if the television is in an unavailable broadcast transmission state or in unavailable broadcast transmission areas. However, in a conventional digital transmission system, there are no methods for effectively adding the additional data other than generating transmission streams in which the additional data are encoded.